Pressure-sensitive recording materials utilizing the color-forming reaction of a color former (a substance forming color on donating an electron or on accepting a proton, such as an acid) and a color developer (a substance accepting an electron or donating a proton, such as clay substances, e.g., acid clay, activated clay, attapulgite, zeolite, bentonite, and kaolin, aromatic carboxylic acid metal salts, and a phenol-formaldehyde resin) are well known, as described in, for example, U.S. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457, 3,418,250, Japanese Patent Publication (unexamined) Nos. 28411/74 and 44009/75.
In addition, printing methods for forming a colored image by applying an ink containing a color former onto a sheet with a color developer coated thereon are known (see German Patent Application (OLS) No. 1,939,962).
As described above, various color developers are known to be used in the preparation of pressure-sensitive recording materials.
When, however, clays such as activated clay and acid clay, which are widely used as a color developer at present, are used, the final color-forming member suffers from various disadvantages; for example, light resistance and water resistance are poor, and storage stability is also poor.
It is known that aromatic carboxylic acid metal salts are free from the problems as described above.
Color developer sheets using such aromatic carboxylic acid metal salts are generally prepared by mechanically dispersing a mixture of the color developers, inorganic pigments, binders, dispersants, and other additives in water to prepare a coating solution and coating the coating solution on a support.
Japanese Patent Publication (unexamined) No. 143322/79 discloses a method of forming a color developer sheet in which the color developer is dissolved in an organic solvent and emulsified in water to prepare a coating solution, and the coating solution thus prepared is coated on a support. A pressure-sensitive recording sheet utilizing the color developer sheet as prepared by the foregoing method has the advantage that the color developer reacts efficiently with the color former; therefore, the sheet exhibits superior color-forming properties even by using a small amount of color developer. It has been revealed, however, that the pressure-sensitive recording sheet suffers from the serious disadvantage that the coated surface is uneven or has irregularities, which is due to the very poor stability of the emulsion. Furthermore, the color-forming rate of the sheet is not always sufficiently satisfactory. Hence, it has been desired to overcome these problems.